Fabrication And Application Of Polymer Modified Electrodes

The interest in chemically modified electrodes (CMEs) has increased tremendously during the last decade owingto their potential applications. The terminology, definitions and preparation methods of CMEs have been described and classified. CMEs have been founded numerous important applications in, e.g., solar energy conversion and storage, selective electro-organic synthesis, molecular electronics, electrochromic display devices, corrosion protection, and electroanalysis.In our papers, a copolymerization of trans-ferulic acid with aniline in acid media was obtained. It was found that the resulted polymer was self-doped one that exhibited a stable electroactivity even in neutral and weakly basic media. It suggested that trans-ferulic acid in oxidized state could react with the radicals of aniline and produce a composite polymer. Moreover, the catalysis of epinephrine could be obtained at this polymer modified electrode. As a consequence, such a modified electrode could be further developed for the clinical applications.A stable electroactive thin film of poly(caffeic acid) has been deposited on the surface of a glassy carbon electrode by potentiostatic technique in a pH 7.0 phosphate buffer containing caffeic acid. The poly(caffeic acid)/glassy carbon electrode is easy to be prepared with good stability and reproducibility. The voltammetric behavior of ascorbic acid (AA), epinephrine (EP), dopamine (DA), serotonin (5-HT) and uric acid (UA) alone or simultaneous some of them at the poly(caffeic acid) modified glassy carbon electrode was studied by cyclic voltammetry. The modified electrode exhibited a high stability whenever it was placed in dry state or in phosphate buffer. No loss of electroactivity of the electrode was found for the continuously cyclically sweep for 8 hours. The modified electrode was also not deteriorated even for long two months.It has been found that the catalytic current of AA depends on the concentration and pH of AA. At pH 7.7, the oxidation peak current of AA on the modified electrode is the maximum. The oxidation peak current is proportional to the AA concentration in the range of 4.0x10~5 to 2.0x10"2 mol/L and a detection limit for AA is 1.0xl0~5 mol I"1. In a pH 7.4 phosphate buffer, the anodic current of EP increased linearly with the concentration of EP in the range from 2.0 x IO~6 to 3.0 x 10'4 mol f' and the detection limit for EP was 6.0 x 10"7 mol \'\ At pH 7.0, the oxidation peak current of 5-HT on the modified electrode is the maximum. AA and EP had no interference with the determination under 5-HT the same condition because the oxidative peak potentials of AA and EP were less than those of 5-HT. Without the interference of AA and EP, linear calibration curves of 5-HT are obtained in pH 7.0 phosphate buffer in the range of 2x10"5 to 6*10~5 mol f1 with a detection limit of 0.5 mol I"'. The chemically modified electrode was applied for the measurement of 5-HT in human blood. This modified electrode exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards A A and DA with activation overpotential. For the mixture containing AA and DA, the two compounds can well separated each other at the scan rate of 10 mV s"1 with a potential difference of 135 mV between AA and DA, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 x 10"5- 1.2 x 10^ mol I'1 and 1.0 x 10"6-4.0x 10~5mol I"1, and the detection limits for AA and DA were 9.0 x 10~6 and 4.0 x 10~7 mol P1, respectively. Poly(caffeic acid) was used as a modified electrode for the detection of AA, EP, UA and their mixture by cyclic voltammetry. This modified electrode exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards AA, EP and UA with activation overpotential. For the ternary mixture containing AA, EP and UA, the three compounds can well separated each other at the scan rate of 20 mV s"1 with a potential difference of 156, 132 and 288 mV between AA and EP, EP and UA, and AA and UA, respectively, which was large enough to determine AA, EP and UA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA, EP and UA concentrations in the range of 2.0-x 10"5 - 1.0 x 10"3 mol I"1, 2.0 x IO"6 - 8.0 x 10"5 mol f1 and 5.0 x 10~6-3.0 x 10~4 mol I"1, and the detection limits for AA, EP and UA were 7.0 x 10"6, 2.0 x 10~7 and 6.0 x 10"7 mol f', respectively. The electrochemical behaviors of EP, DA and their mixture have been studied. The oxidation peaks of EP and DA at the poly(caffeic acid) modified glassy carbon electrode appeared at the same potential, but the anodic peak currents of the mixture of DA and EP were almost equal to the sum of individual anodic peak currents of EP and DA, whereas the cathodic peak current only related to the concentration of DAunder appropriate condition. Base on these, the simultaneous voltammetric measurement of EP and DA at the poly(caffeic acid) film modified electrode has been developed. AA had no interference with the simultaneous determination of EP and DA under the same condition because the oxidative peak potential of A A was less than those of DA and EP.A similar stable thin film of ferulic acid has been deposited on the surface of a glassy carbon electrode by potentionstatic technique in a phosphate buffer solution containing ferulic acid. It was used as a modified electrode for detection of a mixture containing AA, DA and UA by cyclic voltammetry. This modified electrode has good activeness and stability. This modified electrode exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards AA, DA and UA with activation overpotential. For the ternary mixture containing AA, EP and UA, the three compounds can well separated each other at the scan rate of 20 mV s'] with a potential difference of 160, 140 and 300 mV between A A and DA, DA and UA, and A A and UA, respectively, which was large enough to determine AA, DA and UA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA, DA and UA concentrations in the range of 2.0><10"6 -8.0*10~5 mol I"1, 5.0*10~6-3.0xl0~4 mol I"1, and the detection limits for AA, DA and UA were 7.0xl0"6 mol \'\ 2.0xl0~7moir',6.0xl0~7mol 1"'.